The present invention relates to rotors for dynamoelectric machines, and more particularly to improved ventilation for rotors of the non-salient pole type.
Non-salient pole rotors have cylindrical rotor cores carrying windings disposed in longitudinal slots in the outer periphery of the core. The core is normally laminated and, in the usual construction, the core is made up of a series of packs of laminations with spacers between them to form radial ventilating ducts spaced apart longitudinally throughout the length of the core. Longitudinal passages are also usually provided communicating with the radial ducts, and ventilating air flows axially through the longitudinal passages and radially through the ducts to remove heat from the core. In one type of construction, the longitudinal passages are formed between radial arms on the shaft or on a spider member mounted on the shaft. An annular laminated core is supported on the ends of the radial arms which extend longitudinally for the length of the core, and the air passages thus extend under the core and communicate with the radial ducts of the core.
In the conventional design of such rotors, the longitudinal passages, which serve as headers for ventilating air, are of uniform dimensions from one end to the other, and air is forced through them either by an external fan or by a pumping action of the rotor itself so that the air flows longitudinally through the passages and radially through the ventilating ducts of the core. This type of construction has been widely used and in many cases gives satisfactory results. Careful study and analysis of the air flow in this type of rotor, however, has shown that substantial non-uniformities in air flow and in the temperature of the rotor may exist. Thus, in some designs with constant dimensions of the longitudinal air passages, as described above, the radial velocity of air flow through the ventilating ducts of the core may be as much as four times as great at one end of the core as at the other. This difference in air velocity results in a difference in temperature between the two ends of the core which is too great to be acceptable, in many cases, since such a severe temperature gradient across the laminated core may result in serious stress problems and other difficulties.